a = [1, 2, 3]
b = a
a.append(4)
print(b)
print(id(None))

l1 = [a, 1, 2, 3]
l2 = list(l1)
l3 = l1[:]
print(l1 is l2)
print(l1 is l3)
print(l1[0] is l2[0])
print(l1[0] is l3[0])
# 使用list()或[:]是浅复制！

l1 = [3, [66, 55, 44], (7, 8, 9)]
l2 = list(l1)
l1.append(100)
l1[1].remove(55)
print('l1:', l1)
print('l2:', l2)
l2[1] += [33, 22]
l2[2] += (10, 11)
print('l1:', l1)
print('l2:', l2)
# 十分别扭的一个例子！

a = [10, 20]
b = [a, 30]
a.append(b)
print(a)
# 无限循环！其实是C中常见的现象

t1 = (1, 2, 3)
t3 = (1, 2, 3)
print(t3 is t1)
s1 = 'ABC'
s2 = 'ABC'
print(s2 is s1)
